linux-ext4 - Re: [e2fsprogs PATCH] resize2fs: use directio when reading superblock

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Message-ID: <20230609042239.GA1436857@mit.edu>
Date:   Fri, 9 Jun 2023 00:22:39 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Krister Johansen <kjlx@...pleofstupid.com>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [e2fsprogs PATCH] resize2fs: use directio when reading superblock

On Wed, Jun 07, 2023 at 11:50:41AM -0700, Krister Johansen wrote:
> The growpart / resize2fs in the reproducer are essentially verbatim from
> our system provisioning scripts.  Unless those modify the UUID, we're
> not taking any explicit action to do so.

Ah, OK.  OK, I'm guessing that your system provisioning scripts are
attempting mess with the file system a lot (creating, deleting, etc.)
files while trying to run resize2fs in parallel, then?

As far as your patch is concerned, resize2fs can do both off-line
(unmounted) and on-line (mounted) resizes.  And turning direct I/O
unconditionally isn't a great idea for off-line resizes --- it will
really trash the performance of the resize.  Does this patch work for
you instead?

					- Ted

diff --git a/resize/main.c b/resize/main.c
index 94f5ec6d..f914c050 100644
--- a/resize/main.c
+++ b/resize/main.c
@@ -409,6 +409,8 @@ int main (int argc, char ** argv)

 	if (!(mount_flags & EXT2_MF_MOUNTED) && !print_min_size)
 		io_flags = EXT2_FLAG_RW | EXT2_FLAG_EXCLUSIVE;
+	if (mount_flags & EXT2_MF_MOUNTED)
+		io_flags |= EXT2_FLAG_DIRECT_IO;

 	io_flags |= EXT2_FLAG_64BITS | EXT2_FLAG_THREADS;
 	if (undo_file) {